(a) Describe the processes that occur from the time a pollen grain is deposited on the stigma of a flower to the . formation of a zygote.
(b) Explain the importance of the amniotic sac to the mammalian embryo.
(c) The following are the names of some common diseases; malaria, typhoid, amoeboid dysentry, tuberculosis, tetanus, leprosy, cholera, yellow fever, poliomyelitis, measles, common cold, small pox, influenza, chicken pox, whooping cough and trypanosomiasis. Use the format below to classify the diseases according to their causative organisms.
| Viral diseases | Bacteria diseases | Protozoa diseases |
Explanation
(a) Formation of zygote in a flower takes place in the following ways:
- The pollen grain absorbs water, sugary fluid and glucose from sticky stigma.
- It swells and germinates.
- Pollen tube emerges, carrying a tube nucleus and a generative nucleus.
- The generative nucleus divides into two male nuclei; it grows down the style and ovary wall.
- It derives energy and food from the tissues, to reach the ovule; It enters ovule through the micropyle; to enter embryo sac;
- Pollen tube releases male nuclei into embryo sac; as tube nucleus degenerates.
- Nucleus of one male gamete fuses with the egg cell in order to achieve fertilization which resulted to the formation of zygote.
(b) Importance of Amniotic sac are as follows:
(i) Amniotic fluid contains the embryos.
(ii) This provides a constant warm temperature for the foetus.
(iii) It provides a sterile environment for development.
(iv) It provides hydrostatic protection against mechanical injury and shock
(v) It allows movement of the foetus.
| Viral disease (viruses) | Bacteria diseases (Bacteria) | Protozoan diseases (protozoa) |
| yellow fever | Tetanus | malaria |
| poliomyelitis | Typhoid | Trypanosomiasis |
| measles | tuberculosis | Ameoboid dysentery |
| common cold | Leprosy | |
| small pox | cholera | |
| Influenza | whooping cough | |
| chicken pox |